Bonding resins

ABSTRACT

Phenol/aldehyde resins particularly phenol/formaldehyde resins are manufactured by replacing a proportion of the phenol content by a mixture of at least two different natural materials having a phenolic content. The resulting resins which can be used in bonding composite materials are at least as effective as the resin using only phenol and more satisfactory environmentally.

This application claims the benefit of Ser. No. 60/104,784, filed Oct.19, 1998.

This invention relates to bonding resins and particularly to the use ofrenewable resources in or as substitutes for formaldehyde-based resins.

The wood products industry is still almost entirely dependent onchemicals derived from petroleum and natural gas for producing thenecessary bonding agents. The application of bonding agents enables theuse of smaller trees, wood chips, fibers and mill residues to producevarious products that meet the consumer needs. As the quality ofharvested timber declines due to the shrinking commercial forest landbase, the future of wood utilization will require an even higherdependence on bonding agents to convert the limited timber resourcesinto needed products. In view of the environmental strains caused byfossil fuels and chemicals and their inherent vulnerable and limitedsupply, the efforts to identify other available resources for bondingraw materials have accelerated in the latest decades. Renewableresources are he most promising in this field and much research anddevelopment have been devoted in this area.

Formaldehyde-based resins (urea-formaldehyde (UF), phenol-formaldehyde(PF), melanine-formaldehyde (MF), melamine-urea-formaldehyde (MUF),resorcinol-formaldehyde (RF), tannin-formaldehyde (TF) and mixturesthereof) are most commonly applied in composite wood panel manufacture.The components of these resins are mainly derived from oil and/ornatural gas. It is the aim of the present application to provideeffective resin substitutes derived from natural products such asrenewable forest biomass and agricultural residues.

Numerous studies were based on the role of products of natural origin inproviding alternative feedstocks for wood adhesives. Chen, C. M.,“Gluability of Copolymer Resins Having Higher Replacement of Phenol bySouthern Pine Foliage Extracts for Flakeboards and Composite Panels”,Holzforschung, 1993, 47 (1), 72-75, “State of the Art Report: Adhesivesfrom Renewable Resources”, Holzforschung und Holzverwertung, 1996, 4,58-60, “A Hulluva Switch: Inventor Finds Value in Peanut Hulls”, TheUniversity of Georgia, Research Reporter, 12-13, reported that extractsof peanut hulls, pecan nut pith or pine bark and foliage can be used toreplace up to 80% of the phenol used for phenol-formaldehyde resins. Theextraction process involved several stages and was time-consuming.

Efforts have been made also to utilize the oil obtained by the pyrolysisof biomass or its phenolic fraction to substitute phenol in theproduction of phenol-formaldehyde resins, Gallivan, R. M., Matschei, P.K., “Fractionation of Oil obtained by Pyrolysis of LignocellulosicMaterials to recover a Phenolic Fraction for use in makingPhenol-Formaldehyde Resins”, U.S. Pat. No. 4,209,647, 1980; Diebold, J.,Power, A., “Engineering Aspects of the cortex Pyrolysis Reactor toProduce Primary Pyrolysis Oil Vapors or Use in Resins and Adhesives”,Research in Thermochemical Biomass conversion, Bridgwater, A. V.,Kuester, J. L., Elsevier Applied Science, London, 1988, 609-628; Chum,H. L., Diebold, J. P., Scahill, J. W., Johnson, D. K., Black, S.,Schroeder, H. A., Kreibich, R. E., “Biomass Pyrolysis Oil Feedstocks forPhenolic Adhesives”, Adhesives from Renewable Resources, R. Hemingwayand A. Conner, Eds., ACS Symp. Series, No. 385, 1989, 135-151; Chum, H.L., Black, S. K., “Process for Fractionating Fast-Pyrolysis Oils, andProducts derived therefrom”, U.S. Pat. No. 4,942,269, 1990; Chum, H. L.,et alk. “Inexpensive Phenol Replacements from Biomass”, Energy fromBiomass and Wastes XV, Eds. Klass, D. L., 1991, 531-540. Substitutionlevels of up to 75% have been reported, however the low amount ofphenolic compounds present in the oil necessitates a factionation step,which raises the final product cost.

The spent liquor obtained from the paper manufacturing process,comprising mainly the degradation products of lignin, has been thesubject of a large number of studies relating to its applicability informaldehyde-based adhesive systems (mainly PF-adhesives), Forss, K. J.,Fuhrmann, A., “Finnish Plywood, Particleboard, And Fibreboard Made Witha Lignin-Base Adhesive”, Forest Prod. J., 1979, 29 (7), 36-43; Doering,G. A., Harbor, G., “Lignin Modified Phenol-Formaldehyde Resins”, U.S.Pat. No. 5,202,403; Chen, C. M., “Gluability of raft Lignin CopolymerResins on Bonding Southern Pine Plywood”, Holzforschung, 1995, 49 (2),153-157; Senyo, W. C., Creamer, A. W., Wu, C. F., Lora, J. H., “The Useof Organosolv Lignin to Reduce Press Vent Formaldehyde Emissions in theManufacture of Wood Composites”, Forest Prod. J., 1996, 46 (6), 73-77.Various replacement scenarios have been tested, yet the low reactivityof this Liquor cannot justify its use without including any additionalmodification steps.

In the use of these materials single products have been employed andattempts to improve performance have been made by modification of thematerial usually to try and increase the phenolic content.

According to the present invention there is provided a phenol/aldehyderesin system in which a significant proportion of the phenol componentconventionally employed in such resin is replaced by a mixture of atleast two different natural phenolic materials.

The invention also provides a method of forming composite materials inwhich a proportion of the phenol/aldehyde resin component is replaced bya phenol/aldehyde resin system of the invention.

An advantage of the invention is that it permits lowering of resintoxicity by use of the natural substitutes now specified instead oftoxic petroleum derived phenolic products. Thus the phenol/aldehyderesin system of the invention provides an advantage in that it enablesreplacement of conventional phenol materials even though the propertiesof the resin system are not superior to those achieved by normal phenolmaterials.

The phenol/aldehyde resin systems which can be modified in accordancewith this invention are those which are conventional in the manufactureof bonding agents and adhesives. The term “bonding agent” is usedgenerically to include adhesive materials. The most common of theseresins is, of course, phenol/formaldehyde but phenol can be replaced byother materials within the generic term phenol for example cresol orresorcinol to the extent that this is conventional in thephenol/aldehyde resin art and formaldehyde can be replaced by certainother aldehydes although this is not so common In the art. Those skilledin the art of using phenol/aldehyde resins will be well aware of thealternatives and combinations available. The choice of phenois andaldehydes will normally be related to the types of resins employed forthe bonding of composite products but he invention is also applicable tophenol/aldehyde resins employed in other bonding and adhesive functions.

Each of the natural phenolic materials which are used in partsubstitution of the phenol component of the conventional phenol/aldehyderesin will be derived from a natural source. The difference betweenthese materials can arise from the nature of the source or from avariation in treatment of the same natural source so as to providematerials with different properties for example the nature of thephenolic compounds or their proportion. Each of the materials will have,however, a significant content of phenolic components. The phenoliccontent can be free phenols or phenolic groupings in molecules formingpart of the material. By phenolic content is meant the presence in themolecular structure of one or more components (eg. polymeric components)of phenol structures, i.e. hydroxy substituted aromatic groupings ormolecular groupings exhibiting the characteristic properties of phenols.Phenol may be present but usually the component is a compound with aphenolic grouping. Since the natural materials employed in forming thecombinations of the invention are often derived from lignin, a naturalpolymer containing phenolic groups in the structure, extracts, ormodifications of such materials will contain phenolic content. Thematerial can be a natural plant derived material or by-product ofprocessing a natural material. The phenolic content can be the normalcontent or an enhanced content. Enhancement of the phenolic content canbe achieved by various treatments of natural materials, particularlylignins for example extraction or pyrolysis.

Thus each component of the system can be a biomass pyrolysis oil or aspent liquor obtained from a paper manufacturing process or othermanufacturing process applied to natural materials which containphenolic containing components. Thus there could be used extractionproducts of forest biomass or agricultural residues including tropicalspecies residues.

Although thee invention is directed to at least two different naturalphenolic materials there could be more than two materials, each materialcould comprise a mixture of two or more materials. One very suitablecomponent would be a natural product which contains a significant andlarge proportion of phenolic material for example certain nut shell oilsparticularly cashew nut shell liquid. A number of natural productmaterials and by-products are known which contain significant contentsof phenolic components. As mentioned above these can be for examplelignins.

It is surprising to find that, by combining at least two differentnatural materials containing a proportion of phenolic components theresulting combination demonstrates a synergistic effect and enablessubstitution levels of up to 80% of the phenolic component of a standardformaldehyde-based resin. From another point of view, therefore, theinvention lies in the combination of at least two different naturalmaterials, both of which contain phenolic compounds as a substitute forthe phenolic component of a phenol/aldehyde resin. It is surprising tofind that the simple combination of phenolic materials gave animprovement more than would have been expected by the mere increase inhe content of phenolic components. It is surprising to find thatcombination of natural phenolic materials gives en improvement which ismore than would have been expected by the change, particularly anyincrease in the content of phenolic component.

The different Phenolic components can be simply blended when it isdesired to employ them or can be subjected to conditions which causeinteraction between the components.

The substitute composition can be used in the synthesis of the resinsfor bonding the final composite material or can be used in the actualproduction of composite panel products. Although the invention relatesprimarily to the formation of composite materials using bonding agentsprepared with such combinations, improvements have been found for otherbonding or adhesive systems employing formaldehyde-based resinsespecially phenol-formaldehyde resins.

The compositions of the invention can be used in combination with othernatural materials such as tannin to obtain a totally natural resinproduct.

The amount of the phenolic content materials employed can be determinedby adding increasing amounts of one phenolic material to a differentmaterial to the point at which a distinct improvement in the bondingproperties or adhesiveness is noted, particularly in a cured finalcomposite material. Increasing the content of one phenolic materialbeyond a certain proportion is not advantageous since the bonding oradhesiveness obtained will not significantly be advantageous over use ofnormal phenolic materials used in such resins. In other words, theamount of each phenolic material added is determined by the increase insynergistic effect as compared to simply adding one phenolic material toresins. The amounts added can therefore be readily determined by oneskilled in the art. Thus adding one material may allow substitution ofphenol up to a certain percentage by weight and beyond that adeterioration of the composite product properties is observed. It issurprising to find that the combination of several natural derivativesof phenolic character can allow up to 80% phenol substitution withoutimpairment of the composite properties.

The formaldehyde and/or natural resins of the present invention can beapplied in the manufacture of composite panel products such asparticleboard, fibreboard [medium density fibreboard (MDF), high densityfibreboard (HDF)], oriented strand board (OSB) and plywood.

It is also the subject of the invention to use combinations of thedisclosed substitutes with formaldehyde and/or natural resins such astannin resins and other binders such as polymeric diphenyl-methanediisocyanate (PMDI).

The following examples illustrate the invention without limiting itsscone and application.

The Comparative Examples 1 to 3 illustrate the addition of a singlephenolic natural material. Example 1 onwards illustrate the mixtures ofnatural phenolic materials in accordance with the invention.

COMPARATIVE EXAMPLE 1

A series of phenol-formaldehyde resins was synthesised using 0, 10, 20and 40% substitution of the phenol needed in the formula with the liquidobtained by the pyrolysis of wood residues. The resins were subsequentlymixed with wood chips, which were then formed to mats and hot-pressed,to enable the production of 16 mm lab scale particleboards. The resinLevel employed was 12% w/w based on wood chips and 2% K₂CO₃ w/w based onresin solids was applied, to catalyse resin polymerisation reaction. Thepressing temperature and time were 200° C. and 14 s/mm respectively,while the specific press pressure was 3 Kg/cm². The target board densitywas 700 kg/m³. Three replicate boards were produced in each case andtheir properties were subsequently determined. The average values ofboard properties are presented below:

% Substitution 0 10 20 40 IB, N/mm²⁽¹⁾ 0.93 0.98 0.94 0.88 Density,kg/m³ 741 748 745 742 24 h swelling, % 16.7 16.0 16.6 19.5 V100, N/mm²⁽²⁾ 0.47 0.52 0.39 0.28 MOR, N/mm² ⁽³⁾ 26.4 24.4 23.3 20.1 MOR aftertest, N/mm² ⁽⁴⁾ 9.6 5.2 5.2 4.3 HCHO, mg/100 g board 2.1 1.4 1.3 1.0Moisture, % 7.2 7.3 8.0 7.7 ⁽¹⁾Internal Bond strength/tensile strength⁽²⁾IB value after boiling of the samples at 100° C. for 2 h ⁽³⁾Modulusof Rupture/bending strength ⁽⁴⁾MOR value after boiling of the samples at100° C. for 2 h

The formaldehyde (HCHO) emission was determined by using the Perforatormethod.

As it can be seen from the above test, the board properties are improvedby substituting 10% of phenol with pyrolysis liquid. At 20% substitutionthe board properties are acceptable, however they are affectednegatively when higher amount of phenol is replaced.

COMPARATIVE EXAMPLE 2

A series or phenol-formaldehyde resins was synthesised using 0, 10 and20% substitution of the phenol needed in the formula with cashew nutshell liquid (CNSL). The resins were subsequently mixed with wood chips,which were then formed to mats and hot-pressed, to enable the productionof 16 mm lab scale particleboards. The board production conditions werethe same as above. The average values of board properties are presentedbelow:

% Substitution 0 10 20 IB, N/mm² 0.93 0.98 0.97 Density, kg/m³ 741 751750 24 h swelling, % 16.7 15.6 16.2 V100, N/mm² 0.47 0.56 0.42 MOR,N/mm² 26.4 27.7 24.3 MOR after test, N/mm² 8.2 8.5 9.4 HCHO, mg/100 g2.1 1.7 2.5 Moisture, % 7.2 7.7 7.6

In this test, the board properties are improved also by substituting 10%of phenol with CNSL but it is obvious that substitution levels higherthan 20% have a detrimental effect on board properties.

COMPARATIVE EXAMPLE 3

A series of phenol-formaldehyde resins was synthesised using 0, 5, 10and 20% substitution of the phenol needed in the formula with spentliquor obtained from the alkaline pulping of wood matter. The resinswere subsequently applied in the production of 16 mm lab scaleparticleboards. The board production conditions were the same as above.The average values of board properties are presented below:

% Substitution 0 5 10 20 IB, N/mm² 0.87 1.02 0.96 0.55 Density, kg/m³758 742 746 725 24 h swelling, % 13.1 14.0 13.9 15.9 V100, N/mm² 0.310.33 0.36 0.12 MOR, N/mm² 19.4 24.7 22.1 16.8 MOR after test, N/mm² 7.37.4 6.8 4.8 HCHO, mg/100 g board 2.6 2.5 1.8 1.8 Moisture, % 7.7 7.9 8.27.1

The above results indicate that even at 20% substitution of phenol withalkaline pulping spent liquor the board properties are worsened.

EXAMPLE 1

A series of phenol-formaldehyde resins was synthesised using 0, 20 and40% substitution of the phenol needed in the formula with pyrolysisliquid (PL) and 40% substitution of phenol with a mixture of PL and CNSLas well as with a mixture of PL, CNSL and alkaline pulping spent liquor.(SL). The resins were subsequently applied in the production of 16 mmLab scale particleboards. The board production conditions were the sameas above. The average values of board properties are presented below:

% Substitution Natural 0 20 40 40 40 substitutes 0 PL PL PL/CNSLPL/CNSL/SL IB, N/mm² 0.82 0.55 0.55 0.77 0.88 Density 728 709 703 714741 24 h swelling, 14.1 15.1 15.8 14.7 16.2 % V100, N/mm² 0.29 0.19 0.140.31 0.39 MOR, N/mm² 24.4 21.2 20.5 27.8 27.5 MOR after test, 7.7 7.36.7 6.8 7.3 N/mm² HCHO, mg/ 2.8 2.2 2.1 1.5 1.1 100 g board Moisture, %8.1 8.1 7.1 7.9 8.2

The results of this test clearly indicate that the combination of atleast two natural derivatives provides a higher level of phenolsubstitution with optimum board properties as compared to singlesubstitutes applied.

EXAMPLE 2

A series of phenol-formaldehyde resins was synthesised using 0 and 50%substitution of the phenol needed in the formula with a mixture ofpyrolysis liquid (PL) and CNSL as well as with a mixture of PL, CNSL andalkaline pulping spent liquor (SL). The resins were subsequently appliedin the production of 16 mm lab scale particleboards. The boardproduction conditions were the same as above. The average values ofboard properties are presented below:

% Substitution 0 50 50 Natural substitutes 0 PL/CNSL PL/CNSL/SL IB,N/mm² 0.71 0.53 0.76 Density, kg/m³ 736 721 726 24 h swelling, % 17.419.8 18.1 V100, N/mm² 0.30 0.18 0.27 MOR, N/mm² 25.2 19.7 23.5 MOR aftertest, N/mm² 7.4 3.4 7.0 HCHO, mg/100 g 2.4 2.2 1.5 Moisture, % 8.4 6.87.7

The above results confirm all previous findings, since the combinationof three different natural derivatives provides a high phenolsubstitution level with optimum board properties.

EXAMPLE 1

A phenol-formaldehyde resin was synthesised using 40% substitution ofthe phenol needed in the formula with a mixture of pyrolysis liquid,CNSL and alkaline pulping spent liquor. The resin was further applied inthe production of 16 mm lab scale oriented strand board (OSB) incomparison with a standard phenolic resin. The resin level employed was6.5% w/w based on wood strands and 2% K₂CO₃ w/w based on resin solidswas applied, to catalyse resin polymerisation reaction. Mobilcer730 waxemulsion (60%) was also applied at a quantity of 1% w/w based on woodstrands. The pressing temperature and time were 200° C. and 16 s/mmrespectively. The target board density was 660 kg/m³. Three replicateboards were produced in each case and their properties were subsequentlydetermined. The average values of board properties are presented below:

40% of phenol substi- Resin Standard tuted by PL/CNSL/SL IB, N/mm² 0.550.55 Density, kg/m³ 661 681 24 h swelling, % 19.4 18.0 V100, N/mm² 0.240.24 V100 option 2, N/mm² ⁽¹⁾ 0.44 0.52 MOR, N/mm² 23.7 23.9 MOR aftertest, N/mm² 10.8 10.5 HCHO, mg/100 g 1.19 1.11 Moisture, % 4.27 5.29⁽¹⁾V100 measurement after drying and sanding of the samples

In the case of OSB production, the phenolic resin produced bysubstituting 40% of phenol with a mixture of PL, CNSL and SL providesboards with properties equivalent to the ones of the standard resin.

EXAMPLE 4

Phenol-formaldehyde resins were synthesised using 0 and 50% substitutionof the phenol needed in the formula with a mixture of pyrolysis liquid(PL) and CNSL as well as with a mixture of PL, CNSL and alkaline pulpingspent liquor (SL). The resins were further applied in the production oflab scale plywood boards. Three layer composites were produced fromocume veneers, which had been dried to 5-7% moisture prior to plywoodproduction. The glue factor was 150 g/m² and the quantity of the gluemixture needed to cover each side of the middle veneer, was calculatedbased on the dimensions of each particular veneer and the gluing mixtureconcentration. The composites were subjected to a cold pre-pressing at20° C. and 10 kg/cm² for 10 min before the hot pressing. The hotpressing took place at 150° C. and the press time was 3 min at 18Kg/cm². The composite boards obtained were cut to pieces of 20×10 cmsize. Three pieces of each board were immersed in boiling water for 1024, 48, 72 and 96 hours respectively and then submitted to the knifetest. The % wood failure found after the knife test is presented below:

50% phenol 50% phenol substitution substitution Resin Standard withPL/CNSL with PL/CNSL/SL 24 h 100-100 100-100  60-100 48 h 100-100100-100  90-100 72 h 100-100 100-100 100-100 96 h 100-100 100-100100-100

The properties of plywood produced with a phenolic resin, substituted bya mixture of natural derivatives at 50% level (phenol substitution),were found to be equal to the ones or the control. This indicates thatproperties comparable with those of normal phenol/formaldehyde resinscan be achieved using high proportions of natural materials.

What is claimed is:
 1. A phenol/aldehyde resin system in which asignificant proportion of the phenol component conventionally employedin such resin is replaced by a mixture of at least two natural phenolicdifferentiable materials obtained from different source materials or bydifferent production techniques.
 2. A system according to claim 1wherein the phenol/aldehyde resin system is a phenol/formaldehyde resinand at least 40% by weight of the phenol component is replaced by themixture of at least two different natural phenolic materials.
 3. Asystem according to claim 1 wherein the relative proportion of thedifferent natural phenolic materials provides a superiority in bondingproperties in a composite product as compared to a resin system in whichthe phenol component is replaced by the same amount by weight of asingle natural phenolic material.
 4. A resin system according to claim 1wherein the different natural phenolic materials are different membersof the group biomass pyrolysis oils, cashew nut shell liquid, andalkaline pulping spent liquor.
 5. A system according to claim 1 whereinthe proportion of phenol component replaced is from 40% to 80% byweight.
 6. A resin system according to claim 1 in which resin iscombined with another different bonding resin to form the final bondingsystem.
 7. A resin system according to claim 6 in which the otherdifferent bonding resin system is selected from tannin resins and/ordiphenyl-methane diisocyanate resins.
 8. A resin bonding systemaccording to claim 1 which is the bonding system in a composite panelproduct.
 9. A resin according to claim 8 wherein the composite productis a particleboard, a medium density fibreboard, a high densityfibreboard, an oriented strand board or plywood.
 10. A method ofmanufacturing a phenol/aldehyde resin system for bonding compositeproducts wherein at least 40% by weight of the phenol in thephenol/aldehyde resin is replaced by a mixture of at least two differentnatural phenolic materials.
 11. In a phenol aldehyde resin suitable forbonding a composite product wherein the resin comprises a petroleumderived phenol component and an aldehyde component, the improvementwherein at least 20% by weight of the phenol component is replaced witha mixture of at least first and second natural phenolic materials withthe first natural phenolic material being a natural plant material or aby-product of a natural plant material and the second natural phenolicmaterial being a different natural plant material or by-product of anatural plant material, the at least first and second natural phenolicmaterials being selected and being present in the resin in respectiveamounts sufficient to effect a synergistic result in bonding thecomposite product such that the resin provides improved bonding in thecomposite product as compared to a resin in which the phenol componentis replaced by the same amount by weight of the first or second naturalphenolic material singly.
 12. The phenol aldehyde resin of claim 11,wherein the first and second natural phenolic materials are differentmembers or by-products of the group consisting of a biomass pyrolysisoil, a cashew nut shell liquid, and alkaline pulping spent liquor. 13.The phenol aldehyde resin of claim 11, wherein at least 40% by weight ofthe phenol component is replaced with the mixture of the at least firstand second natural phenolic materials.
 14. The phenol aldehyde resin ofclaim 13, wherein the phenol component is replaced with a mixture ofthree different natural phenolic materials or by-products thereof. 15.The phenol aldehyde resin of claim 14, wherein the three differentnatural phenolic materials respectively comprise a pyrolysis liquid, acashew nut shell liquid, and an alkaline pulping spent liquor.